1. Field of the Invention
The present invention relates to a guide or deflecting unit for a tension member at a structural component of a structure extending outside of the cross-section of the structure, wherein the tension member extends with a change of direction over a deflection point formed at the structural component.
2. Description of the Related Art
When constructing structures of prestressed concrete, particularly in the case of bridge structures, prestressing is carried out with and without adhesion. Prestressing with adhesion is usually carried out as prestressing with subsequent adhesion, wherein the tension members are located within the cross-section of the concrete and adhesion to the structure is effected by injecting cement paste after the tension members have been tensioned. In the case of prestressing without adhesion, the tension members are located outside of the cross-section of the concrete, but are supported relative to the structure. As a result, these tension members, also called external tension members, can be checked, retensioned and also exchanged as necessary at any time. External tension members are also frequently used for rehabilitating or subsequently reinforcing bridges.
In external tension members, which extend essentially outside of the cross-section of the concrete, it is usually not possible to adapt the axis of the tension member continuously curved to the pattern of the bending moments; rather, it is necessary that the tension member follow a polygonal course. This produces guide or deflecting locations where deflection forces directed toward the inner side of the curvature must be absorbed.
In the case of greater angles of deflection, it is necessary for avoiding a kink in the course of the tension member to provide in the area of a deflection location a deflection saddle which has a curvature corresponding to the radius of curvature of the tension member, so that a soft absorption of the deflection forces is achieved.
In this connection, it is known in the art to use a steadily curved tube, particularly curved in the shape of a circular arc, through which the tension member extends in the area of a deflection location (DE 37 34 954 C2). Although the manufacture and assembly of such a curved tube is complicated, this configuration is acceptable if it is used in a structure to be newly manufactured and the curved tube can be accurately dimensioned and placed in the concrete. This configuration is too complicated if, for rehabilitating or reinforcing an existing structure, a curved tube must be placed, for example, into a bore and the hollow space remaining between the bore and the tube must be filled with hardening material, so that a problem-free transmission of the deflection forces is ensured. This produces additional requirements and delays the construction.
Therefore, in view of the prior art discussed above, it is the primary object of the present invention to provide a simple and economical possibility for ensuring a problem-free absorption of the deflection forces at the points of deflection of external tension members.
In accordance with the present invention, the guide or deflection unit is composed of a tubular shaped piece of a deformable material which surrounds the tension member and whose contour is shaped in the longitudinal direction such that its wall thickness decreases from the middle toward the ends in accordance with the curvature of the required deflection, so that the predetermined curvature is obtained when tensioning the tension member by the contact thereof with a wall of a straight receiving means.
Consequently, the basic concept of the invention resides in that a shaped piece surrounding the tension member is provided, wherein the outer contour of the shaped piece corresponds in the direction of the tension member axis with a negative sign to the radius of curvature of the deflection saddle to be provided and which, when the tensioning force is applied to the respective tension member, can be deformed together with the tension member in such a way that by contacting the wall of the straight receiving means the required deflection saddle is achieved. As a result, the guide or deflection unit according to the present invention can be used with particular advantage in the rehabilitation of bridges because it is only necessary for producing a deflection point to provide a straight receiving means, for example, a straight bore produced by core drilling. The desired deflection radius then automatically is produced with the correct magnitude independently of any existing tolerances. Since a dry assembly is possible, the assembly is inexpensive and fast.
In accordance with a useful feature of the present invention, the shaped piece is composed of a section of a tube of synthetic material, especially PE. In the case of such a tube, it is easily possible to produce the required con tour by processing, particularly by turning. If the wall thickness of a tube is not sufficient for accommodating the camber of the curvature of a deflection location, it is also possible to slide two or more tube sections concentrically onto one another, wherein the inner portion of the respectively inner tube has the normal wall thickness, while the required contour is provided at the tube sect ion placed over the inner tube.
Since external tension members usually have a circular cross-section, it is useful if the shaped piece according to the present invention also has a circular cross-section. However, the shaped piece may also have a rectangular cross-section or may be composed of individual plates which surround the tension member.
In order to achieve in all cases a complete contact of the shaped piece with the sheathing tube surrounding the tension member, it is useful to cut the shaped piece open in the longitudinal direction or, in the case of shaped pieces having greater diameters, to cut out an appropriate strip from the shaped piece. On the one hand, this makes it easier to carry out the assembly and, on the other hand, this produces the result that the shaped piece completely surrounds the tension member as a result of the restoring forces inherent in the synthetic material.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.